Consistency in diagnosis between two clinicians looking at the same patient

Test re-test

Repetition of a diagnosis assessed by testing the same person twice with a gap of weeks or months and diagnosis should be the same

Beck et al (1962)

The agreement on diagnosis for 153 patients between two psychiatrists was only 54%

Cooper et al (1972)

NY psychiatrists 2x as likely to diagnose schiz - London psychiatrists 2x as likely to diagnose mania or depression

Brown

67% agreement rate for major depression

Davison and Neale (1994)

92% agreement rate for psychosexual disorders, but only 54% for somatoform disorders

Zigler and Phillips (1961)

54-84% agreement rate when looking at various mental illnesses

Nicholls et al

Compared reliability of DSM IV, ICD 10 & The Great Ormond Street's classification system for children with eating disorders

ICD - 36% agreement DSM - 64% GOS - 88%

Validity

Criterion

When two or more diagnostic systems agree with each other e.g. DSM and ICD-10

Concurrent

Symptoms that form part of the disorder but are not part of the actual diagnosis, should be found in the diagnosed e.g. people with schizophrenia having poor personal hygiene

Etiological

A group of people who have been diagnosed with the same disorder will have the same factors causing it e.g. schiz - excess dopamine

Predictive

If diagnosis can lead to a prediction of future behaviours caused by the disorder

E.g. the drug lithium carbonate is effective for bipolar disorder but not other mental disorders. If a classification system has good predictive validity and diagnoses someone with bipolar, they should respond to lithium carbonate